Systems, devices, and methods for laser projectors

ABSTRACT

Laser safety systems, devices, and methods for use in laser projectors are described. A laser projector includes any number of laser diodes that each emit laser light, a laser diode power source, a current sensor to detect a magnitude of the electric current output by the power source, a photodetector to detect a power/intensity of the laser light, a beam splitter to direct a first portion of the light towards the photodetector and a second portion of the light towards an output on the projector, and first and second laser safety circuits responsive to signals from the photodetector and the current sensor, respectively. The laser safety circuits selectively electrically couples/uncouples the laser diodes from the power source depending on signals from the photodetector and/or the current sensor. Particular applications of the laser safety systems, devices, and methods in a wearable heads-up display are described.

TECHNICAL FIELD

The present systems, devices, and methods generally relate to laserprojectors and particularly relate to the safety of laser projectors.

BACKGROUND Description of the Related Art

Laser Projectors

A projector is an optical device that projects or shines a pattern oflight onto another object (e.g., onto a surface of another object, suchas onto a projection screen) in order to display an image or video onthat other object. A projector necessarily includes a light source, anda laser projector is a projector for which the light source comprises atleast one laser. The at least one laser is temporally modulated toprovide a pattern of laser light and usually at least one controllablemirror is used to spatially distribute the modulated pattern of laserlight over a two-dimensional area of another object. The spatialdistribution of the modulated pattern of laser light produces an imageat or on the other object. In conventional scanning laser projectors,the at least one controllable mirror may include: a single digitalmicromirror (e.g., a microelectromechanical system (“MEMS”) baseddigital micromirror) that is controllably rotatable or deformable in twodimensions, or two digital micromirrors that are each controllablyrotatable or deformable about a respective dimension, or a digital lightprocessing (“DLP”) chip comprising an array of digital micromirrors.

Laser Safety

Malfunction or improper use of laser devices can result in temporary orpermanent damage to the eye; therefore, laser safety precautions areessential. Safety measurements for lasers and laser devices include: themaximum permissible exposure (MPE) (i.e., the maximum amount of userexposure before damage occurs), and the accessible emission limit (AEL)(i.e., the emitted power of the laser that is accessible in use). MPE ismeasured as power density (W/cm² or J/cm²) and AEL is measured as power(W or J) or power density (W/cm² or J/cm²) depending on the specificlaser wavelength.

Wearable Heads-Up Displays

A head-mounted display is an electronic device that is worn on a user'shead and, when so worn, secures at least one electronic display within aviewable field of at least one of the user's eyes, regardless of theposition or orientation of the user's head. A wearable heads-up displayis a head-mounted display that enables the user to see displayed contentbut also does not prevent the user from being able to see their externalenvironment. The “display” component of a wearable heads-up display iseither transparent or at a periphery of the user's field of view so thatit does not completely block the user from being able to see theirexternal environment. Examples of wearable heads-up displays include:the Google Glass®, the Optinvent Ora®, the Epson Moverio®, and the SonyGlasstron®, just to name a few.

The optical performance of a wearable heads-up display is an importantfactor in its design. When it comes to face-worn devices, however, usersalso care a lot about aesthetics. This is clearly highlighted by theimmensity of the eyeglass (including sunglass) frame industry.Independent of their performance limitations, many of the aforementionedexamples of wearable heads-up displays have struggled to find tractionin consumer markets because, at least in part, they lack fashion appeal.Most wearable heads-up displays presented to date employ large displaycomponents and, as a result, most wearable heads-up displays presentedto date are considerably bulkier and less stylish than conventionaleyeglass frames.

A challenge in the design of wearable heads-up displays is to minimizethe bulk of the face-worn apparatus while still providing displayedcontent with sufficient visual quality. There is a need in the art forwearable heads-up displays of more aesthetically-appealing design thatare capable of safely providing high-quality images to the user withoutintroducing unreasonable risk to the user's eye(s).

BRIEF SUMMARY

A laser projector may be summarized as including: at least one laserdiode; a photodetector responsive to laser light output by the at leastone laser diode; a current sensor responsive to electric current outputby a power source; a beam splitter positioned and oriented to direct afirst portion of laser light from the at least one laser diode along afirst optical path towards the photodetector and a second portion oflaser light from the at least one laser diode along a second opticalpath towards an output of the laser projector; a first laser safetycircuit communicatively coupled to the photodetector and responsive tosignals therefrom, the first laser safety circuit comprising a firstswitch that mediates an electrical coupling between the power source andthe at least one laser diode, wherein in response to a signal from thephotodetector indicative that a power of the laser light output by theat least one laser diode exceeds a first threshold, the first switchinterrupts a supply of power to the at least one laser diode from thepower source; and a second laser safety circuit communicatively coupledto the current sensor and responsive to signals therefrom, the secondlaser safety circuit comprising a second switch that mediates electricalcoupling between the power source and the at least one laser diode,wherein in response to a signal from the current sensor indicative thatan electric current output by the power source exceeds a secondthreshold, the switch interrupts a supply of power to the at least onelaser diode from the power source. The laser projector optionallyincludes the power source, or the power source is supplied separatelytherefrom, for example by a consumer or end user of the laser projector.

The first laser safety circuit may further include a first latch that iscommunicatively coupled to the photodetector and to the first switch,wherein: a state of the first latch is responsive to signals from thephotodetector and the first switch is responsive to the state of thefirst latch; the state of the first latch changes from a first state toa second state in response to the signal from the photodetectorindicative that the power of the laser light output by the at least onelaser diode exceeds the first threshold; and the first switch interruptsthe supply of power to the at least one laser diode from the powersource in response to the state of the first latch changing from thefirst state to the second state. The first latch may be operable tostore a current state selected from the first state and the second stateand maintain the current state during a reboot event. The laserprojector may further include: a processor communicatively coupled tothe at least one laser diode and to the first latch, the processor tomodulate the at least one laser diode, wherein, in response to the latchbeing in the second state, the processor stops modulating the at leastone laser diode and prevents further modulations of the at least onelaser diode. The laser projector may further include a non-transitoryprocessor-readable storage medium communicatively coupled to theprocessor, wherein: in response to the first latch being in the secondstate, the processor stores a flag in the non-transitoryprocessor-readable storage medium; and upon boot-up of the laserprojector, the processor accesses the non-transitory processor-readablestorage medium to check for the flag, wherein in response to theprocessor finding the flag stored in the non-transitoryprocessor-readable storage medium the processor prevents modulations ofthe at least one laser diode.

The second laser safety circuit may further include a second latch thatis communicatively coupled to the current sensor and to the secondswitch, wherein: a state of the second latch is responsive to signalsfrom the current sensor and the second switch is responsive to the stateof the second latch; the state of the second latch changes from a firststate to a second state in response to the signal from the currentsensor indicative that the electric current output by the power sourceexceeds the second threshold; and the second switch interrupts thesupply of power to the at least one laser diode from the power source inresponse to the state of the first latch changing from the first stateto the second state. The second latch may be operable to store a currentstate selected from the first state and the second state and maintainthe current state during a reboot event. The laser projector may furtherinclude: a processor communicatively coupled to the at least one laserdiode and to the second latch, the processor to modulate the at leastone laser diode, wherein, in response to the second latch being in thesecond state, the processor stops modulating the at least one laserdiode and prevents further modulations of the at least one laser diode.The laser projector may further comprise a non-transitoryprocessor-readable storage medium communicatively coupled to theprocessor, wherein: in response to second latch being in the secondstate the processor stores a flag in the non-transitoryprocessor-readable storage medium; and upon boot-up of the laserprojector, the processor accesses the non-transitory processor-readablestorage medium to check for the flag, wherein in response to theprocessor finding the flag stored in the non-transitoryprocessor-readable storage medium the processor prevents modulations ofthe at least one laser diode. The laser projector may further include: adigital potentiometer to set the second threshold; and a comparatorcommunicatively coupled to the digital potentiometer and communicativelycoupled in between the current sensor and the latch, the comparator tocompare signals from the current sensor to the second threshold set bythe digital potentiometer and to control the state of the latch based ona comparison between at least one signal from the current sensor and thesecond threshold set by the digital potentiometer.

The second laser safety circuit of the laser projector may furtherinclude a digital potentiometer to set the second threshold.

A method of operating a laser projector comprising a power source, atleast one laser diode, a beam splitter, a photodetector, a currentsensor, and a first laser safety circuit and a second laser safetycircuit which operate simultaneously, may be summarized as including:providing power to the at least one laser diode by the power sourceelectrically coupled to the at least one laser diode; generating a laserlight by the at least one laser diode; splitting the laser light into afirst portion and a second portion by the beam splitter; directing thefirst portion of the laser light from the at least one laser diode alonga first optical path towards a photodetector by the beam splitter;directing the second portion of the laser light from the at least onelaser diode along a second optical path towards an output of the laserprojector by the beam splitter; detecting the first portion of the laserlight by the photodetector; outputting a first signal by thephotodetector in response to detecting the first portion of the laserlight by the photodetector, the first signal indicative of a power ofthe laser light generated by the at least one laser diode; receiving thefirst signal from the photodetector by the first laser safety circuitcommunicatively coupled to the photodetector, wherein the first lasersafety circuit includes a first switch that mediates the electricalcoupling between the power source and the at least one laser diode; andin response to the first signal from the photodetector indicating thatthe power of the laser light generated by the at least one laser diodeexceeds a first threshold, interrupting, by the first switch, a supplyof power to the at least one laser diode from the power source; anddetecting the electric current output of the power source by the currentsensor; outputting a second signal indicative of the electric currentoutput of the power source by the current sensor, receiving the secondsignal from the current sensor by the second laser safety circuitcommunicatively coupled to the current sensor, wherein the second lasersafety circuit includes a second switch that mediates the electricalcoupling between the power source and the at least one laser diode; andin response to the second signal from the current sensor indicating thatelectric current output of the power source exceeds a second threshold,interrupting, by the second switch, a supply of power to the at leastone laser diode from the power source.

The first laser safety circuit may include a first latch that iscommunicatively coupled to the photodetector and to the first switch,wherein a state of the first latch is responsive to the signal from thephotodetector and the first switch responsive to the state of the firstlatch, and the method may further include: in response to the signalfrom the photodetector indicating that the power of the laser lightoutput by the at least one laser diode exceeds the first threshold,changing, by the first latch, the state of the first latch from a firststate to a second state; and wherein interrupting, by the first switch,a supply of power to the at least one laser diode from the power sourceincludes interrupting, by the first switch, a supply of power to the atleast one laser diode from the power source in response to the state ofthe first latch changing from the first state to the second state. Themethod may further include: storing a current state of the first latch;and maintaining the current state of the first latch during a rebootevent.

The laser projector may include a processor, wherein the processor iscommunicatively coupled to the first latch, and wherein generating alaser light by the at least one laser diode includes modulating the atleast one laser diode by the processor, and the method may furtherinclude: in response to the state of the first latch indicating that thepower of the laser light generated by the at least one laser diodeexceeds the first threshold: stopping modulation of the at least onelaser diode by the processor; and preventing further modulations of theat least one laser diode by the processor. The laser projector mayinclude a non-transitory processor-readable storage mediumcommunicatively coupled to the processor, and the method may furtherinclude: in response to the state of the first latch indicating that thepower of the laser light generated by the at least one laser diodeexceeds the first threshold, storing, by the processor, a flag in thenon-transitory processor-readable storage medium; and upon boot-up ofthe laser projector, checking for the flag stored in the non-transitoryprocessor-readable storage medium by the processor and, in response tofinding the flag stored in the non-transitory processor-readable storagemedium by the processor, preventing modulations of the at least onelaser diode by the processor.

The second laser safety circuit may include a second latch that iscommunicatively coupled to the current sensor and to the second switch,wherein a state of the second latch is responsive to the signal from thecurrent sensor and the second switch responsive to the state of thesecond latch, and wherein the method further includes: in response tothe signal from the current sensor indicating that the electric currentoutput by the power source exceeds the second threshold, changing, bythe second latch, the state of the second latch from a first state to asecond state; and wherein interrupting, by the second switch, a supplyof power to the at least one laser diode from the power source includesinterrupting, by the second switch, a supply of power to the at leastone laser diode from the power source in response to the state of thesecond latch changing from the first state to the second state. Themethod may further include: storing a current state of the second latch;and maintaining the current state of the second latch during a rebootevent. The laser projector may include a processor, the processorcommunicatively coupled to the second latch, wherein generating a laserlight by the at least one laser diode includes modulating the at leastone laser diode by the processor, and the method further including: inresponse to the state of the second latch indicating that the electriccurrent output of the power source exceeds the second threshold:stopping modulation of the at least one laser diode by the processor;and preventing further modulations of the at least one laser diode bythe processor. The laser projector may include a non-transitoryprocessor-readable storage medium communicatively coupled to theprocessor, and the method may further include: in response to the stateof the second latch indicating that the electric current output of thepower source exceeds the second threshold, storing, by the processor, aflag in the non-transitory processor-readable storage medium; and uponboot-up of the laser projector, checking for the flag stored in thenon-transitory processor-readable storage medium by the processor and,in response to finding the flag stored in the non-transitoryprocessor-readable storage medium by the processor, preventingmodulations of the at least one laser diode by the processor.

The laser projector may further include a digital potentiometer, and themethod may further include setting the second threshold by the digitalpotentiometer.

A wearable heads-up display (“WHUD”) may be summarized as including: asupport structure that in use is worn on the head of a user; atransparent combiner carried by the support structure and positioned ina field of view of at least one eye of the user when the supportstructure is worn on the head of the user; and a laser projector carriedby the support structure and positioned and oriented to direct laserlight towards the transparent combiner, the laser projector comprising:at least one laser diode; a power source; a photodetector responsive tolaser light output by the at least one laser diode; a current sensorresponsive to electric current output by the power source; a beamsplitter positioned and oriented to direct a first portion of laserlight from the at least one laser diode along a first optical pathtowards the photodetector and a second portion of laser light from theat least one laser diode along a second optical path towards an outputof the laser projector; a first laser safety circuit communicativelycoupled to the photodetector and responsive to signals therefrom, thefirst laser safety circuit comprising a first switch that mediates anelectrical coupling between the power source and the at least one laserdiode, wherein in response to a signal from the photodetector indicativethat a power of the laser light output by the at least one laser diodeexceeds a first threshold, the first switch interrupts a supply of powerto the at least one laser diode from the power source; and a secondlaser safety circuit communicatively coupled to the current sensor andresponsive to signals therefrom, the second laser safety circuitcomprising a second switch that mediates an electrical coupling betweenthe power source and the at least one laser diode, wherein, in responseto a signal from the current sensor indicative that an electric currentoutput of the power source exceeds a second threshold, the second switchinterrupts a supply of power to the at least one laser diode from thepower source.

The first laser safety circuit of the laser projector may furtherinclude a first latch that is communicatively coupled to thephotodetector and to the first switch, wherein: a state of the firstlatch is responsive to signals from the photodetector and the firstswitch is responsive to the state of the first latch; the state of thefirst latch changes from a first state to a second state in response tothe signal from the photodetector indicative that the power of the laserlight output by the at least one laser diode exceeds the firstthreshold; and the first switch interrupts the supply of power to the atleast one laser diode in response to the state of the first latchchanging from the first state to the second state. The first latch maybe operable to store a current state selected from the first state andthe second state and maintain the current state during a reboot event.The WHUD may further include a processor communicatively coupled to theat least one laser diode and to the first latch, the processor tomodulate the at least one laser diode, wherein, in response to the latchbeing in the second state, the processor stops modulating the at leastone laser diode and prevents further modulations of the at least onelaser diode. The WHUD may further include a non-transitoryprocessor-readable storage medium communicatively coupled to theprocessor, wherein: in response to the first latch being in the secondstate, the processor stores a flag in the non-transitoryprocessor-readable storage medium; and upon boot-up of the laserprojector, the processor accesses the non-transitory processor-readablestorage medium to check for the flag, wherein in response to theprocessor finding the flag stored in the non-transitoryprocessor-readable storage medium the processor prevents modulations ofthe at least one laser diode.

The second laser safety circuit may further include a second latch thatis communicatively coupled to the current sensor and to the secondswitch, and wherein: a state of the second latch is responsive tosignals from the current sensor and the second switch is responsive tothe state of the second latch; the state of the second latch changesfrom a first state to a second state in response to the signal from thecurrent sensor indicative that the electric current output by the powersource exceeds the second threshold; and the second switch interruptsthe supply of power to the at least one laser diode from the powersource in response to the state of the first latch changing from thefirst state to the second state. The second latch may be operable tostore a current state selected from the first state and the second stateand maintain the current state during a reboot event. The WHUD mayfurther include a processor communicatively coupled to the at least onelaser diode and to the second latch, the processor to modulate the atleast one laser diode, wherein, in response to the second latch being inthe second state, the processor stops modulating the at least one laserdiode and prevents further modulations of the at least one laser diode.The WHUD may further include a non-transitory processor-readable storagemedium communicatively coupled to the processor, wherein: in response tosecond latch being in the second state the processor stores a flag inthe non-transitory processor-readable storage medium; and upon boot-upof the laser projector, the processor accesses the non-transitoryprocessor-readable storage medium to check for the flag, wherein inresponse to the processor finding the flag stored in the non-transitoryprocessor-readable storage medium the processor prevents modulations ofthe at least one laser diode. The second laser safety circuit of theWHUD may further include a digital potentiometer to set the secondthreshold; and a comparator communicatively coupled to the digitalpotentiometer and communicatively coupled in between the current sensorand the latch, the comparator to compare signals from the current sensorto the second threshold set by the digital potentiometer and to controlthe state of the latch based on a comparison between at least one signalfrom the current sensor and the second threshold set by the digitalpotentiometer.

The second laser safety circuit of the WHUD may further include adigital potentiometer to set the second threshold.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not necessarily drawn to scale, and some ofthese elements are arbitrarily enlarged and positioned to improvedrawing legibility. Further, the particular shapes of the elements asdrawn are not necessarily intended to convey any information regardingthe actual shape of the particular elements, and have been solelyselected for ease of recognition in the drawings.

FIG. 1 is a schematic diagram of a laser projector with a first lasersafety circuit and a second laser safety circuit in accordance with thepresent systems, devices, and methods.

FIG. 2A is a schematic diagram of a first laser safety circuit for alaser projector, the laser safety circuit shown in a configuration inwhich the at least one laser diode of the projector is electricallyuncoupled from the power source in accordance with the present systems,devices, and methods.

FIG. 2B is a schematic diagram of a second laser safety circuit for alaser projector, shown in a configuration in which the at least onelaser diode of the projector is electrically uncoupled from the powersource in accordance with the present systems, devices, and methods.

FIG. 3A is a flow diagram showing a method of operating a laserprojector with a first laser safety circuit in accordance with thepresent systems, devices, and methods.

FIG. 3B is a flow diagram showing a method of operating a laserprojector with a second laser safety circuit in accordance with thepresent systems, devices, and methods.

FIG. 4 is partial cutaway perspective view of a wearable heads-updisplay with a laser projector and associated first laser safety circuitand second laser safety circuit in accordance with the present systems,devices, and methods.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedembodiments. However, one skilled in the relevant art will recognizethat embodiments may be practiced without one or more of these specificdetails, or with other methods, components, materials, etc. In otherinstances, well-known structures associated with portable electronicdevices and head-worn devices, have not been shown or described indetail to avoid unnecessarily obscuring descriptions of the embodiments.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its broadest sense, that is as meaning “and/or”unless the content clearly dictates otherwise.

The headings and Abstract of the Disclosure provided herein are forconvenience only and do not interpret the scope or meaning of theembodiments. The various embodiments described herein provide systems,devices, and methods for safe operation of a laser projector and areparticularly well-suited for use in near eye displays (e.g., wearableheads-up displays (“WHUDs”)) that employ laser projectors.

FIG. 1 is a schematic diagram of a laser projector 100 with a firstlaser safety circuit and a second laser safety circuit in accordancewith the present systems, devices, and methods. Laser projector 100comprises, for example, four laser diodes 110 a, 110 b, 110 c, 110 d(collectively 110), a beam combiner 120, a photodetector 131 responsiveto light emitted by each of laser diodes 110, at least one scan mirror140, a current sensor 151, a laser diode power source 160 electricallycoupled to laser diodes 110, and a processor 170 communicatively coupledto both laser diodes 110 and photodetector 131. The first laser safetycircuit of laser projector 100 includes a first latch (e.g.,“flip-flop”) 132 communicatively coupled to photodetector 131 and afirst switch 133 that is communicatively coupled to latch 132 andelectrically coupled in between power source 160 and laser diodes 110.The second laser safety circuit of laser projector 100 includes a secondlatch 152 that is communicatively coupled to current sensor 151 and asecond switch 153 that is communicatively coupled to latch 153 andelectrically coupled in between power source 160 and laser diodes 110.Processor 170 is communicatively coupled to both latch 132 and latch153. Processor 170 (i.e., circuitry), can take the form of one or moreof any of microprocessors, microcontrollers, application specificintegrated circuits (ASICs), digital signal processors (DSPs),programmable gate arrays (PGAs), and/or programmable logic controllers(PLCs), or any other integrated or non-integrated circuit that performlogic operations).

Throughout this specification and the appended claims, the terms“electrical coupling” and “communicative coupling” (and variants, suchas “electrically coupled” and “communicatively coupled”) are often used.Generally, “electrical coupling” refers to any engineered arrangementfor coupling electrical signals between one or more electrical signalcarrier(s) (e.g., conductor(s) or semiconductor(s)) and includes withoutlimitation galvanic coupling, inductive coupling, magnetic coupling,and/or capacitive coupling for the purpose of transferring, for example,electrical data signals, electrical information, and/or electricalpower. Electrical coupling is a form of communicative coupling.“Communicative coupling” refers to any engineered arrangement fortransferring signals (e.g., electrical or otherwise) for the purpose oftransferring data, information, and/or power and includes, at least,electrical coupling (e.g., via electrically conductive wires,electrically conductive traces), magnetic coupling (e.g., via magneticmedia), and/or optical coupling (e.g., via optical fiber).

In brief, the first laser safety circuit of projector 100 operates asfollows. Signals output by photodetector 131 control a state of latch132 and the state of latch 132 controls a state of switch 133. Switch133 is controllably switchable into and between a first state orconfiguration in which electrical coupling between power source 160 andlaser diodes 110 is enabled by or through switch 133 and a second stateor configuration in which electrical coupling between power source 160and laser diodes 110 is disabled by or through switch 133. Laser diodes110 consist of a first red laser diode (R), a second green laser diode(G), a third blue laser diode (B), and a fourth infrared laser diode(IR). All four laser diodes 110 are selectively electrically coupleableto power source 160 by or through at least one switch 133 and arecommunicatively coupled to the processor 170 that controls the operation(e.g., modulation) thereof. The first laser diode 110 a emits a first(e.g., red) light signal 111, the second laser diode 110 b emits asecond (e.g., green) light signal 112, the third laser diode 110 c emitsa third (e.g., blue) light signal 113, and the fourth laser diode 110 demits a fourth (e.g., infrared) light signal 114. All four of lightsignals 111, 112, 113, and 114 enter or impinge on beam combiner 120comprising optical elements 121, 122, 123, and 124. First light signal111 is emitted towards first optical element 121 and reflected by firstoptical element 121 of beam combiner 120 towards second optical element122 of beam combiner 120. Second light signal 112 is also directedtowards second optical element 122. Second optical element 122 is formedof a dichroic material that is transmissive of the red wavelength offirst light signal 111 and reflective of the green wavelength of secondlight signal 112; therefore, second optical element 122 transmits firstlight signal 111 and reflects second light signal 112. Second opticalelement 122 combines first light signal 111 and second light signal 112into a single aggregate beam (shown as separate beams for illustrativepurposes) and routes the aggregate beam towards third optical element123 of beam combiner 120. Third light signal 113 is also routed towardsthird optical element 123. Third optical element 123 is formed of adichroic material that is transmissive of the wavelengths of light(e.g., red and green) in the aggregate beam comprising first lightsignal 111 and second light signal 112 and reflective of the bluewavelength of third light signal 113. Accordingly, third optical element123 transmits the aggregate beam comprising first light signal 111 andsecond light signal 112 and reflects third light signal 113. In thisway, third optical element 123 adds third light signal 113 to theaggregate beam such that the aggregate beam comprises light signals 111,112, and 113 (shown as separate beams for illustrative purposes) androutes the aggregate beam towards fourth optical element 124 in beamcombiner 120. Fourth light signal 114 is also routed towards fourthoptical element 124. Fourth optical element 124 is formed of a dichroicmaterial that is partially transmissive of the visible wavelengths oflight (e.g., red, green, and blue) in the aggregate beam comprisingfirst light signal 111, second light signal 112, and third light signal113 and partially reflective of the infrared wavelength of fourth lightsignal 114. Accordingly, fourth optical element 124 partially transmitsthe aggregate beam comprising first light signal 111, second lightsignal 112, and third light signal 113 and partially reflects fourthlight signal 114. In this way, fourth optical element 124 adds at leasta portion of fourth light signal 114 to the aggregate beam such that theaggregate beam comprises portions of light signals 111, 112, 113, and114 and routes at least a portion of the aggregate beam towards scanmirror 140 and the output of projector 100.

In the exemplary implementation of projector 100, fourth optical element124 is a dual-purpose optical component. In addition to functioning asthe last optical combining element in optical combiner 120 (i.e., bycombining fourth, infrared laser light 114 with the red, green, and bluelaser light 111, 112, and 113, respectively), fourth optical element 124also functions as a beam splitter in projector 100. To this end, fourthoptical element 124 is positioned and oriented to direct a first portion115 of the aggregate laser light (represented by a dashed arrow inFIG. 1) from laser diodes 110 (i.e., comprising first light 111, secondlight 112, third light 113, and fourth light 114) towards photodetector130 and a second portion 116 of the aggregate laser light (alsorepresented by a dashed arrow in FIG. 1) towards scan mirror 140 and anoutput of laser projector 100. In the implementation of FIG. 1, scanmirror 140 scans (e.g., raster scans) second portion 116 of theaggregate laser beam to output a projected display or illuminationpattern. In the implementation of a wearable heads-up display, scanmirror 140 may direct the visible light to create display content in thefield of view of a user, and may direct the infrared light to illuminatethe eye of the user for the purpose of eye tracking. A person of skillin the art will appreciate that the visible and infrared light may takedifferent paths before or beyond the scan mirror. A person of skill inthe art will also appreciate that methods other than a scan mirror, suchas beam steering and/or one or more digital light processor(s), can beemployed to create display content or to direct the infrared light.

Photodetector 131 is responsive to first portion 115 of the aggregatelaser beam and, in response to detecting first portion 115 of theaggregate laser beam, outputs a signal indicative of, based on,dependent on, or generally representative of the power or intensity offirst portion 115 of the aggregate laser beam. In an implementation withmultiple laser sources (e.g., multiple laser diodes 110), each lasersource emitting light of a different wavelength or a different range ofwavelengths (e.g., laser light signals 111, 112, 113, and 114),photodetector 131 is responsive to light within one or more waveband(s)that, in total (e.g., collectively in combination) includes all of theemitted wavelengths. Latch 132 is communicatively coupled tophotodetector 131 and has a state that is responsive to signalstherefrom. If and/or when a signal from photodetector 131 is below afirst threshold, latch 132 is in a first state; if and/or when a signalfrom photodetector 131 is above a first threshold, latch 132 is in asecond state. Latch 132 may be operable to store and maintain (i.e.,keep or reload) its current state if a reboot event occurs. For example,if a signal indicative of laser light that exceeds the first thresholdcaused latch 132 to be in the second state, the latch would still be inthe second state following a reboot event unless the latch is positivelycleared, via a separate action by the user that is not part of anautomated or autonomous process of rebooting. Switch 122 iscommunicatively coupled to and responsive to the state of latch 132. Asignal that indicates the state of latch 132 is received by switch 133from latch 132. Switch 133 is selectively electrically coupleablebetween power source 160 and laser diodes 110. Switch 133controllably/selectively enables or disables electrical coupling betweenpower source 160 and laser diodes 110 in response to the state of latch132. In other words, depending on the state of latch 132 (which itselfdepends on a magnitude of a signal output by photodetector 131,representative of a magnitude of the power or intensity of first portion115 of the aggregate laser beam in projector 100), switch 133selectively provides or blocks (e.g., interrupts) electrical power tolaser diodes 110 from power source 160.

The second laser safety circuit of laser projector 100 operates asfollows. Power source 160 generates an electric current. Current sensor151 is responsive to the electric current output by power source 160 andoutputs a signal indicative of, based on, or generally representative ofthe magnitude of the output current. Latch 152 is communicativelycoupled to current sensor 151 and has a state that is responsive tosignals therefrom. If and/or when a signal from current sensor 151 isbelow a second threshold, latch 152 is in a first state; if and/or whena signal from current sensor 151 is above the second threshold, latch152 is in a second state. Latch 152 may be operable to store andmaintain (i.e., keep or reload) its current state if a reboot eventoccurs. Switch 153 is communicatively coupled to latch 152 andresponsive to the state of latch 152. Switch 153 is electricallycoupleable between power source 160 and lasers diodes 110. Switch 153controllably/selectively enables or disables electrical coupling betweenpower source 160 and one or more of laser diodes 110 in response to thestate of latch 152. That is, when latch 152 is in the firstconfiguration switch 153 enables electrical coupling between powersource 160 and one or more of laser diodes 110, and when latch 152 is inthe second configuration switch 153 disables electrical coupling betweenpower source 160 and one or more of laser diodes 110. Generally, when alaser diode 110 draws higher electric current, the laser diode 110outputs higher intensity laser light. Thus, the second laser safetycircuit is used to disable one or more of laser diodes 110 when thecurrent drawn thereby exceeds the second threshold because having one ormore of laser diodes 110 draw current that exceeds the second thresholdpresent a safety risk to the user.

In some implementations, the second laser safety circuit may be adaptedto monitor the current drawn by each respective one of laser diodes 110and to selectively deactivate any one or all of laser diodes 110 inresponse to a detected current drawn that exceeds the second threshold.Such implementations may employ, for example, a respective currentsensor 151, latch 152, and switch 153 that mediate communicativecoupling between power source 160 and respective ones of laser diodes110.

Both latch 132 and 152 may be communicatively coupled to processor 170and processor 170 may be responsive to the states of latches 132 and152. That is, if either latch 132 or 152 is in the respective secondstate, processor 170 may modulate the laser diodes to output no lightand may prevent any further modulations of laser light from occurring.This provides redundant safety measures if switch 133 or switch 153fails to respond to the respective state of latch 132 or 153 correctly.

Laser projector 100 may include a laser diode driver between powersource 160 and laser diodes 110 which modulates laser diodes 100. Thelaser diode driver may also be responsive to signals from or states ofelements of the first laser safety circuit and the second laser safetycircuit.

Throughout this specification and the appended claims, reference isoften made to a “first threshold” for the maximum safe power/intensityof laser light and a “second threshold” for the maximum safe electricalcurrent (i.e., maximum amperage). The first threshold may be definedbased on a variety of factors including, for example, the wavelength(s)of the laser diode(s) (different wavelengths have different effects onthe eye), the specific portion of light incident on the photodetector,the type of display employed, and/or the efficiency of any interveningoptical elements in the optical path of the laser light between thelaser diode(s) and the display/eye of the user (e.g., scan mirrors,lenses, polarizers, filters, diffractive optical elements). The secondthreshold may also be defined based on a number of factors including,the wavelengths(s) if the laser diode, the efficiency of the conversionof current into laser light by the laser diodes, the safety limit ofamperage in a commercial device, etc. Once defined, these thresholds mayadvantageously be non-varying and independent of any parameters that maychange during the operation of the laser projector, such as the scanrate of a scan mirror (e.g., the scan mirror function may have adiscrete safety mechanism). In some implementations, the thresholds maytake into account any number of failure modes and/or “worst-casescenarios” (such as a mirror failure that causes the laser spot toremain fixed in one place on the user's eye) so that any such failuresor scenarios are accounted for in static, non-varying thresholds withouthaving to introduce additional monitoring and feedback systems.

As an example, the first laser safety circuit (e.g., upstream of thelatch element of the first laser safety circuit) may include a firstcomparator operative to compare the signal coming from the photodetectorto a static threshold value defined as outlined above.

As an example, the second laser safety circuit (e.g., upstream of thelatch element of the second laser safety circuit) may include a secondcomparator operative to compare the signal coming from the currentsensor to a static threshold value defined as outlined above.

As described above, the second threshold(s) for the current(s) drawn byrespective ones or collectively by all of laser diodes 110 may benon-varying for a given physical implementation of the second lasersafety circuit; however, in implementations in which a second lasersafety circuit is deployed in a real, manufactured product (e.g., in aconsumer-ready WHUD), it may be necessary for the second threshold(s)employed to differ from one WHUD to the next. For example, in amanufacturing process that produces scanning laser projectors (or WHUDsthat include scanning laser projectors), even if all the laser diodesused come from the same supplier and with tight tolerances there will beperformance differences from one laser diode to the next. In someinstances, the amount of current that can cause different instances ofthe “same” laser diode to output a dangerous amount of light can vary byaround 50%. For this reason, it can be challenging to employ a secondlaser safety circuit having the same parameters (e.g., the same secondthreshold(s)) across all deployments in different ones of the sameproduct. In order to overcome this challenge, in accordance with thepresent systems, devices, and methods, the second laser safety circuitmay be “trimmable.” That is, the second laser safety may include amechanism that enables the second threshold(s) to be tuned or adjustedbased on the performance characteristics of the particular laserdiode(s) being employed. For example, a digital potentiometer or“digital trim pot” may be included in the second laser safety and usedto set the second threshold(s). The current sensor (e.g., 151) and thedigital potentiometer may both feed into a comparator and the comparatormay compare the incoming current sensor data against a configuredsetting of the digital potentiometer representative of a secondthreshold value. The comparator may then control the state of the latchas previously described. In this implementation, the second threshold isessentially tunable via the digital potentiometer. Thus, duringmanufacture of the device (projector, WHUD, or the like) that employsthe second laser safety circuit, the performance profile of the laserdiode(s) may be determined and the digital potentiometer may be tuned toadjust the second threshold(s) to the appropriate safe level(s) thatcorresponds to the particular laser diode(s) being employed.

The first threshold value for the power of laser light received byphotodetector 131 may be calculated based on the maximum amount of lightthat can be safely received by an eye of a user and the percentage ofattenuation of light through any intervening optical elements of thelaser projector along the optical path between the laser diode(s) andthe eye of the user. For example, the path of light from the laserdiode(s) to the eye may be through the beam splitter, scanned over twoscan mirrors, and redirected from a holographic optical element to theretina of the eye. In this example, if the maximum amount of lightsafely receivable by the eye is 1 mW, the holographic optical elementhas 30% loss of light, the two scan mirrors each lose 5% of the light,and the beam splitter directs 25% of the light to the photodetector,then the maximum power/intensity of light that can be received by thephotodetector without exceeding 1 mW at the eye is 0.52 mW (i.e.0.25×1/(0.7×0.95×0.95×0.75) mW. Thus in this example the threshold valuemay be set at 0.52 mW and the first laser safety circuit may beconfigured to operate in the first configuration (in which the switch isclosed and electrical power is coupled to the laser diodes) when thesignal provided by the photodetector corresponds to less than 0.52 mWdetected by the photodetector and in the second configuration (in whichthe switch is open and the laser diodes are cut-off from the powersource) when the signal provided by the photodetector corresponds togreater than 0.52 mW detected by the photodetector. As a furtherprotective measure, the threshold may be lowered to account for variousfailures modes, such as lowering the threshold by (e.g., 5%, 10%, 25%,50%, depending on the specific implementation) to ensure the laser lightreceived by the eye will be safe even in the event of such a failure(e.g., in the event of a mirror disruption that causes the laser lightto stop sweeping and instead project onto a single point at the user'seye).

In FIG. 1, switches 132 and 152 are shown in an exemplary closedconfiguration indicating electrical coupling of laser diodes 110 andpower source 160, thereby enabling the continued generation of firstportion 115 and second portion 116 of aggregate laser light. FIGS. 2Aand 2B provide illustrative examples of the “switch open” configurationsof the first laser safety circuit and second laser safety circuit,respectively.

FIG. 2A is a schematic diagram of a first laser safety circuit 200 a fora laser projector, the laser safety circuit shown in a configuration inwhich the at least one laser diode 210 of the projector is electricallyuncoupled from a power source 260 in accordance with the presentsystems, devices, and methods. In the illustrated example of FIG. 2A,photodetector 231 detects a laser light signal above the firstthreshold, and consequently outputs an above first threshold signal.Latch 232 has received an above first threshold signal fromphotodetector 231 and entered into the second state or configuration(represented by shading of latch 232 in FIG. 2A). Switch 233 hasresponded to the second state or configuration of latch 232 and hasopened to disable electrical coupling between the at least one laserdiode 210 and power source 260. The at least one laser diode 210 iswithout power (represented by shading of at least one laser diode 210)and cannot emit a laser light signal. The latch may be operable to storethe current state and maintain the state during and after a rebootevent. In the circumstances and configuration of FIG. 2B, the latchwould still be in the second state following a reboot event unless thelatch is positively cleared, via a separate action by the user that isnot part of an automated or autonomous process of rebooting. Electricalcoupling of the power source and laser diodes would remain interrupted.

FIG. 2B is a schematic diagram of a first laser safety circuit 200 b fora laser projector, the laser safety circuit shown in a configuration inwhich the at least one laser diode 210 of the projector is electricallyuncoupled from the power source 260 in accordance with the presentsystems, devices, and methods. In the illustrated example of FIG. 2B,current sensor 251 detects an electrical current output from powersource 260 above the second threshold, and consequently outputs an abovesecond threshold signal. Latch 252 has received an above secondthreshold signal from current sensor 251 and entered into the secondstate or configuration (represented by shading of latch 252 in FIG. 2B).Switch 253 has responded to the second state or configuration of latch252 and has opened to disable electrical coupling between the at leastone laser diode 210 and power source 260. The at least one laser diode210 is without power (represented by shading of at least one laser diode210) and cannot emit a laser light signal. The latch may be operable tostore the current state and maintain the state during and after a rebootevent. In the circumstances and configuration of FIG. 2B, the latchwould still be in the second state following a reboot event unless thelatch is positively cleared, via a separate action by the user that isnot part of an automated or autonomous process of rebooting. Electricalcoupling of the power source and laser diodes would remain interrupted.

FIG. 3A is a flow diagram showing a method 300 a of operating a laserprojector with a first laser safety circuit in accordance with thepresent systems, devices, and methods. The laser projector may besubstantially similar, or even identical, to the laser projector 100from FIG. 1 and the first laser safety circuit may be substantiallysimilar, or even identical, to that used in laser projector 100 and/orfirst laser safety circuit 200 a from FIG. 2A. The laser projectorgenerally includes a power source, at least one laser diode, aphotodetector, and a first laser safety circuit communicatively coupledbetween the photodetector and the power source. Method 300 a comprisesvarious acts 301, 302, 303, 304, 305, 306, 307, and 308 a/b, thoughthose of skill in the art will appreciate that in alternativeembodiments certain acts may be omitted and/or additional acts may beadded. Method 300 a may occur simultaneously with method 300 b describedbelow and shown in FIG. 3B, but is described separately for clarity.Those of skill in the art will also appreciate that the illustratedorder of the acts is shown for exemplary purposes only and may change inalternative embodiments.

At 301, the power source provides power to the at least one laser diode.The power source may be selectively electrically coupled through aswitch to the at least one laser diode, the switch being part of thefirst laser safety circuit and operative to allow or disable power tothe at least one laser diode. At 301, the switch is “closed” to enablecoupling of electrical power therethrough from the power source to thelaser diode(s).

At 302, the at least one laser diode generates laser light using theelectrical power received from the power source.

At 303, a beam splitter directs a first portion of the laser lighttowards a photodetector and a second portion of the laser light towardsan output of the projector. Those of skill in the art will appreciatethat the path of the laser light from the laser diode(s) to beamsplitter may contain several optical elements (i.e., optics) thatreflect, transmit, shape, and/or combine the light. In someimplementations the beam splitter may also act as a combiner ofdifferent laser light beams generated at 302 (as illustrated in theexample of FIG. 1). The light output by the projector may be directedtowards a scan mirror or other element(s) that directs the light toilluminate an area. The area may be a field of view of a user fordisplay purposes or may be an eye of a user for eye tracking purposes.

At 304, the photodetector detects the first portion of light directedfrom the beam splitter at 303. The photodetector is responsive to all ofthe wavelengths of light included in the laser light generated by the atleast one laser diode at 302. An example of a suitable photodetectorhaving such wide optical spectral sensitivity in the ISL58344 QuadSegment Photo Sensor IC from Intersil.

At 305, the photodetector outputs a signal in response to detecting thefirst portion of light from the beam splitter at 304. The photodetectordetects the power (e.g., wattage) and/or intensity of the laser lightand outputs a voltage signal representative of the power and/orintensity. Generally, the voltage of the signal output by thephotodetector is dependent on (e.g., proportional to) the power and/orintensity of the laser light detected by the photodetector at 304. Thesignal from the photodetector may be amplified by one or moreamplifier(s) and/or converted from analog to digital by one or moreanalog-to-digital converter(s).

At 306, the first laser safety circuit receives the signal from thephotodetector. The first laser safety circuit includes communicativecoupling between the photodetector and the power source and may comprisea latch or “flip-flop” communicatively coupled to the photodetector witha state/configuration responsive to the signal from the photodetector,and a switch communicatively coupled to the latch and responsive to thestate/configuration of the latch.

At 307, the first laser safety circuit processes the signal from thephotodetector. If, at 304, the photodetector detects a first portion oflaser light that is below a maximum safe power level, then at 307 thefirst laser safety circuit determines that the signal from thephotodetector (output at 305) is below a first threshold value. On theother hand, if, at 304, the photodetector detects a first portion oflaser light that is at or above the maximum safe power level, then at307 the first laser safety circuit determines that the signal from thephotodetector (output at 305) is above the first threshold value.

From act 307, method 300 a proceeds either to act 308 a or act 308 bdepending on the magnitude of the signal provided, at 305, by thephotodetector relative to the first threshold. In response to the signalreceived from the photodetector by the first laser safety circuit at 306being below a first threshold (e.g., in response to the first lasersafety circuit determining at 307 that the signal received from thephotodetector is below the first threshold), method 300 a proceeds toact 308 a; whereas in response to the signal received from thephotodetector by the first laser safety circuit at 306 being at or abovethe first threshold (e.g., in response to the first laser safety circuitdetermining at 307 that the signal received from the photodetector isabove the first threshold), method 300 a proceeds to act 308 b.

At 308 a, the first laser safety circuit maintains electrical couplingbetween the power source and the at least one laser diode in response tothe signal received from the photodetector at 306 being below the firstthreshold. In an implementation with a latch communicatively coupled tothe photodetector and a switch communicatively coupled to the latch andselectively electrically coupled between the power source and the atleast one laser diode, at 308 a the switch remains closed, maintainingelectrical coupling between the power source and the at least one laserdiode.

Alternatively, at 308 b, the first laser safety circuit disableselectrical coupling between the power source and the at least one laserdiode in response to the signal received from the photodetector at 306being at or above the first threshold. In an implementation with a latchcommunicatively coupled to the photodetector and a switchcommunicatively coupled to the latch and selectively electricallycoupled between the power source and the at least one laser diode, at308 b the switch opens to disable electrical coupling between the powersource and the at least one laser diode and effectively switches off theat least one laser diode.

In an implementation with a latch, the method may comprise additionalacts. These additional acts may include: storing a current state of thelatch, and maintaining the state of the latch during and following areboot event. Following 308 a, the latch would be in a first state andelectrical coupling between the power source and the at least one laserdiode would be intact. Following 308 b, the latch would be in a secondstate and electrical coupling between the power source and the at leastone laser diode would be interrupted. The current state of the latch ismaintained (i.e., kept or reloaded) during and following a reboot eventuntil and unless the latch is positively cleared, via a separate actionby the user that is not part of an automated or autonomous process ofrebooting. If the latch were in a first state before a reboot event, thelatch would remain in the first state following reboot of the laserprojector, and the electrical coupling between the power source and theat least one laser diode would remain intact. Likewise, if the latchwere in a second state before a reboot event, the latch would remain inthe second state following reboot of the laser projector, and theelectrical coupling between the power source and the at least one laserdiode would remain interrupted.

FIG. 3B is a flow diagram showing a method 300 b of operating a laserprojector with a second laser safety circuit in accordance with thepresent systems, devices, and methods. The laser projector may besubstantially similar, or even identical, to laser projector 100 fromFIG. 1 and the second laser safety circuit may be substantially similar,or even identical, to that used in laser projector 100 and/or secondlaser safety circuit 200 b from FIG. 2B. The laser projector generallyincludes a power source, at least one laser diode, a current sensor, anda second laser safety circuit communicatively coupled between thecurrent sensor and the power source. Method 300 b comprises various acts301, 309, 310, 311, 312, 313 a, and 313 b, though those of skill in theart will appreciate that in alternative embodiments certain acts may beomitted and/or additional acts may be added. Method 300 b may occursimultaneously with method 300 a described above and shown in FIG. 3A,but is described separately for clarity. Those of skill in the art willalso appreciate that the illustrated order of the acts is shown forexemplary purposes only and may change in alternative embodiments.

At 301, the power source provides power to the at least one laser diode.The power source may be selectively electrically coupled through aswitch to the at least one laser diode, the switch being part of thesecond laser safety circuit and operative to allow or disable power tothe at least one laser diode. At 301, the switch is “closed” to enablecoupling of electrical power therethrough from the power source to thelaser diode(s).

At 309, the current sensor detects the electrical current output by thepower source.

At 310, the current sensor outputs a signal in response to detecting theelectrical current. The current sensor detects the magnitude of thecurrent (i.e., value of the amperes output by the power source). Thesignal output by the current sensor is indicative of the electricalcurrent output by the power source.

At 311, the second laser safety circuit receives the signal from thecurrent sensor. The second laser safety circuit includes communicativecoupling between the current sensor and the power source and maycomprise a latch or “flip-flop” communicatively coupled to the currentsensor with a state/configuration responsive to the signal from thecurrent sensor, and a switch communicatively coupled to the latch andresponsive to the state/configuration of the latch.

At 312, the second laser safety circuit processes the signal from thephotodetector. If, at 309, the current sensor detects an electricalcurrent below a maximum safe current level, then at 312 the second lasersafety circuit determines that the signal from the current sensor isbelow a second threshold value. On the other hand, if, at 309, thecurrent sensor detects an electrical current that is at or above themaximum safe current level, then at 312 the second laser safety circuitdetermines that the signal from the current sensor is above the secondthreshold value.

From act 312, method 300 b proceeds either to act 313 a or act 313 bdepending on the magnitude of the signal provided by the current sensorrelative to the second threshold. In response to the signal receivedfrom the current sensor by the second laser safety circuit being below asecond threshold (e.g., in response to the second laser safety circuitdetermining at 312 that the signal received from the photodetector isbelow the second threshold), method 300 b proceeds to act 313 a; whereasin response to the signal received from the current sensor by the secondlaser safety circuit being at or above the second threshold (e.g., inresponse to the second laser safety circuit determining at 312 that thesignal received from the photodetector is above the second threshold),method 300 b proceeds to act 313 b.

At 313 a, the second laser safety circuit maintains electrical couplingbetween the power source and the at least one laser diode in response tothe signal received from the current at 311 being below the secondthreshold. In an implementation with a latch communicatively coupled tothe current sensor and a switch communicatively coupled to the latch andselectively electrically coupled between the power source and the atleast one laser diode, at 313 a the switch remains closed, maintainingelectrical coupling between the power source and the at least one laserdiode.

Alternatively, at 313 b, the second laser safety circuit disableselectrical coupling between the power source and the at least one laserdiode in response to the signal received from the current sensor at 311being at or above the second threshold. In an implementation with alatch communicatively coupled to the current sensor and a switchcommunicatively coupled to the latch and selectively electricallycoupled between the power source and the at least one laser diode, at313 b the switch opens to disable electrical coupling between the powersource and the at least one laser diode and effectively switches off theat least one laser diode.

In some implementations, the laser projector may further include adigital potentiometer and method 300 b may include setting the secondthreshold by the digital potentiometer. In such implementations,processing the signal from the current sensor at 312 may includecomparing, e.g., by a comparator communicatively coupled to the digitalpotentiometer and communicatively coupled in between the current sensorand the latch, the signal from the current sensor to the secondthreshold value set by the digital potentiometer.

In an implementation with a latch, the method may comprise additionalacts. These additional acts may include: storing a current state of thelatch, and maintaining the state of the latch during and following areboot event. Following 313 a, the latch would be in a first state andelectrical coupling between the power source and the at least one laserdiode would be intact. Following 313 b, the latch would be in a secondstate and electrical coupling between the power source and the at leastone laser diode would be interrupted. The current state of the latch ismaintained (i.e., kept or reloaded) during and following a reboot eventuntil and unless the latch is positively cleared, via a separate actionby the user that is not part of an automated or autonomous process ofrebooting. If the latch were in a first state before a reboot event, thelatch would remain in the first state following reboot of the laserprojector, and the electrical coupling between the power source and theat least one laser diode would remain intact. Likewise, if the latchwere in a second state before a reboot event, the latch would remain inthe second state following reboot of the laser projector, and theelectrical coupling between the power source and the at least one laserdiode would remain interrupted.

For both method 300 a and method 300 b the laser projector may furtherinclude one or more processor(s) communicatively coupled to both thefirst laser safety circuit and the second laser safety circuit by therespective latches, and one or more non-transitory processor-readablestorage medium (or media) communicatively coupled to the processor(s).The processor(s) may be responsive to the state of the first latch andthe second latch and the method may further include wherein theprocessor(s) modulates the laser diodes to stop outputting laser lightwhen either or both latches are in the respective secondstates/configurations. A flag may be stored in non-transitoryprocessor-readable storage medium (or media) by the processor(s) wheneither or both latches are in the second state/configuration thatprevents modulation of the laser diodes by the processor(s) following areboot event.

As previously described, the laser projector safety systems, devices,and methods described herein are particularly well-suited for use inWHUDs. An illustrative example of a WHUD that employs a laser projectorwith a first laser safety circuit and a second laser safety circuit isprovided in FIG. 4.

FIG. 4 is partial cutaway perspective view of a WHUD 400 with a laserprojector 430 and associated first and second laser safety circuits inaccordance with the present systems, devices, and methods. WHUD 400includes a support structure 470 that in use is worn on the head of auser and has a general shape and appearance of an eyeglasses frame.Support structure 470 carries multiple components, including: a lens471, a transparent combiner 472, and a laser projector. The laserprojector (see magnified view thereof in box) is generally similar, oreven identical, to laser projector 100 from FIG. 1 and includes laserdiodes 410 a beam combiner/splitter 420, a laser diode power source 460selectively electrically coupleable to laser diodes 410, a processor(not shown) to modulate emission of light from laser diodes 410, aphotodetector 431, a current sensor 451, a first laser safety circuit,and a second laser safety circuit. The first laser safety circuitincludes a switch 433 electrically coupled between laser diodes 410 andpower source 460, as well as a first latch (not shown to reduce clutter)communicatively coupled to and between photodetector 431 and switch 433.The second laser safety circuit includes a switch 453 electricallycoupled between laser diodes 110 and power source 460, as well as asecond latch (not shown to reduce clutter) communicatively coupled toand between current sensor 451 and switch 453. The laser projectoroperates in generally the same manner as laser projectors 100 from FIG.1, the first and second laser safety circuits operate in generally thesame manner as the respective first and second laser safety circuits inFIGS. 1, 2A, and 2B. Laser diodes 410 output laser light to beamcombiner 420. Beam combiner 420 combines the laser light from laserdiodes 410 into a single aggregate beam. A first portion of theaggregate beam light is directed towards photodetector 431 and a secondportion of the aggregate light is directed to an output of the laserprojector. Output aggregate laser light may be directed towards a scanmirror to create an image in the field of view of the user.

The first laser safety circuit operates as follows. Photodetector 431detects the first portion of aggregate light from the beam splitter andoutputs a signal based on the power of the light. The first latch has astate/configuration that is responsive to the signal from photodetector431. The first latch remains in a first state/configuration if thesignal from photodetector 431 is below a first threshold and changes toa second state/configuration if the signal from photodetector 431 is ator above a first threshold. The first latch may be operable to store thecurrent state during a reboot event and maintain (i.e., keep or reload)the state after the reboot event until and unless the latch ispositively cleared, via a separate action by the user that is not partof an automated or autonomous process of rebooting. Switch 433 iscommunicatively coupled to and responsive to the state/configuration ofthe first latch. Switch 433 is selectively, electrically coupleablebetween power source 460 and laser diodes 410 and can enable or disableelectrical coupling between power source 460 and laser diodes 410, inresponse to the state/configuration of the first latch.

The second laser safety circuit operates as follows. Current sensor 451detects the magnitude (i.e., the amperage) of the electric currentoutput from power source 460 and outputs a signal indicative of theelectric current. The second latch, which has a state/configuration thatis responsive to the signal from current sensor 451, receives the signalfrom current sensor 451. The second latch remains in a firststate/configuration if the signal from current sensor 451 is below asecond threshold and changes to a second state/configuration if thesignal from current sensor 451 is at or above a second threshold. Thesecond latch may be operable to store the current state during a rebootevent and maintain (i.e., keep or reload) the state after the rebootevent until and unless the second latch is positively cleared, via aseparate action by the user that is not part of an automated orautonomous process of rebooting. Switch 453 is communicatively coupledto and responsive to the state/configuration of the second latch. Switch453 is selectively, electrically coupleable between power source 460 andlaser diodes 410 and can enable or disable electrical coupling betweenpower source 460 and laser diodes 410, in response to thestate/configuration of the second latch.

Both the first latch and the second latch may be communicatively coupledto the processor and the processor may be responsive to the state ofboth latches. That is, if either latch is in the respective secondstate, the processor will respond by modulating laser diodes 410 toproduce no laser light and will not perform any further modulation oflaser light. WHUD 400 may further include a non-transitoryprocessor-readable storage medium which is communicatively coupled tothe processor, and which stores processor executable data and/orinstructions. In response to the first or second latch being in arespective second state/configuration the processor may store a flag inthe non-transitory processor-readable storage medium which, upon areboot event, prevents the processor from modulating the output of lightfrom laser diodes 410.

In some implementations, at least a first processor may becommunicatively coupled to a first set of components (e.g., laser diodes410, the at least one scan mirror, other functionality components ofWHUD 400) for the purpose of controlling operation of the first set ofcomponents and at least a second processor (e.g., a microcontroller) maybe communicatively coupled to the elements (e.g., current sensor 151,latch 152) of the second laser safety circuit for the purpose ofcontrolling operation of the elements of the second laser safetycircuit.

Throughout this specification and the appended claims, the term“carries” and variants such as carried by are generally used to refer toa physical coupling between two objects. The physical coupling may bedirect physical coupling (i.e., with direct physical contact between thetwo objects) or indirect physical coupling mediated by one or moreadditional objects. Thus the term carries and variants such as “carriedby” are meant to generally encompass all manner of direct and indirectphysical coupling.

A person of skill in the art will appreciate that the variousembodiments for laser projectors described herein may be applied innon-WHUD applications. For example, the present systems, devices, andmethods may be applied in non-WHUD and/or in other applications that mayor may not include a visible display.

In some implementations, one or more optical fiber(s) may be used toguide light signals along some of the paths illustrated herein.

The WHUDs described herein may include one or more sensor(s) (e.g.,microphone, camera, thermometer, compass, altimeter, and/or others) forcollecting data from the user's environment. For example, one or morecamera(s) may be used to provide feedback to the processor of the WHUDand influence where on the display(s) any given image should bedisplayed.

The WHUDs described herein may include one or more on-board powersources (e.g., one or more battery(ies)), a wireless transceiver forsending/receiving wireless communications, and/or a tethered connectorport for coupling to a computer and/or charging the one or more on-boardpower source(s).

The WHUDs described herein may receive and respond to commands from theuser in one or more of a variety of ways, including without limitation:voice commands through a microphone; touch commands through buttons,switches, or a touch sensitive surface; and/or gesture-based commandsthrough gesture detection systems as described in, for example, U.S.Non-Provisional patent application Ser. No. 14/155,087, U.S.Non-Provisional patent application Ser. No. 14/155,107, PCT PatentApplication PCT/US2014/057029, and/or U.S. Provisional PatentApplication Ser. No. 62/236,060, all of which are incorporated byreference herein in their entirety.

Throughout this specification and the appended claims, infinitive verbforms are often used. Examples include, without limitation: “to detect,”“to provide,” “to transmit,” “to communicate,” “to process,” “to route,”and the like. Unless the specific context requires otherwise, suchinfinitive verb forms are used in an open, inclusive sense, that is as“to, at least, detect,” to, at least, provide,” “to, at least,transmit,” and so on.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe embodiments to the precise forms disclosed. Although specificembodiments of and examples are described herein for illustrativepurposes, various equivalent modifications can be made without departingfrom the spirit and scope of the disclosure, as will be recognized bythose skilled in the relevant art. The teachings provided herein of thevarious embodiments can be applied to other portable and/or wearableelectronic devices, not necessarily the exemplary wearable electronicdevices generally described above.

For instance, the foregoing detailed description has set forth variousembodiments of the devices and/or processes via the use of blockdiagrams, schematics, and examples. Insofar as such block diagrams,schematics, and examples contain one or more functions and/oroperations, it will be understood by those skilled in the art that eachfunction and/or operation within such block diagrams, flowcharts, orexamples can be implemented, individually and/or collectively, by a widerange of hardware, software, firmware, or virtually any combinationthereof. In one embodiment, the present subject matter may beimplemented via Application Specific Integrated Circuits (ASICs).However, those skilled in the art will recognize that the embodimentsdisclosed herein, in whole or in part, can be equivalently implementedin standard integrated circuits, as one or more computer programsexecuted by one or more computers (e.g., as one or more programs runningon one or more computer systems), as one or more programs executed by onone or more controllers (e.g., microcontrollers) as one or more programsexecuted by one or more processors (e.g., microprocessors, centralprocessing units, graphical processing units), as firmware, or asvirtually any combination thereof, and that designing the circuitryand/or writing the code for the software and or firmware would be wellwithin the skill of one of ordinary skill in the art in light of theteachings of this disclosure.

When logic is implemented as software and stored in memory, logic orinformation can be stored on any processor-readable medium for use by orin connection with any processor-related system or method. In thecontext of this disclosure, a memory is a processor-readable medium thatis an electronic, magnetic, optical, or other physical device or meansthat contains or stores a computer and/or processor program. Logicand/or the information can be embodied in any processor-readable mediumfor use by or in connection with an instruction execution system,apparatus, or device, such as a computer-based system,processor-containing system, or other system that can fetch theinstructions from the instruction execution system, apparatus, or deviceand execute the instructions associated with logic and/or information.

In the context of this specification, a “non-transitoryprocessor-readable medium” can be any element that can store the programassociated with logic and/or information for use by or in connectionwith the instruction execution system, apparatus, and/or device. Theprocessor-readable medium can be, for example, but is not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus or device. More specific examples (anon-exhaustive list) of the computer readable medium would include thefollowing: a portable computer diskette (magnetic, compact flash card,secure digital, or the like), a random access memory (RAM), a read-onlymemory (ROM), an erasable programmable read-only memory (EPROM, EEPROM,or Flash memory), a portable compact disc read-only memory (CDROM),digital tape, and other non-transitory media.

The various embodiments described above can be combined to providefurther embodiments. To the extent that they are not inconsistent withthe specific teachings and definitions herein, all of the U.S. patents,U.S. patent application publications, U.S. patent applications, foreignpatents, foreign patent applications and non-patent publicationsreferred to in this specification and/or listed in the Application DataSheet which are owned by Thalmic Labs Inc., including but not limitedto: US Patent Application Publication No. 2016-0377866 A1 US, US PatentApplication Publication No. 2016-0377865, US Patent ApplicationPublication No. US 2014-0198034 A1, US Patent Application PublicationNo. US 2016-0238845 A1, US Patent Application Publication No. US2014-0198035 A1, Non-Provisional patent application Ser. No. 15/046,234,U.S. Non-Provisional patent application Ser. No. 15/046,254, U.S.Non-Provisional patent application Ser. No. 15/145,576, U.S.Non-Provisional patent application Ser. No. 15/145,609, U.S.Non-Provisional patent application Ser. No. 15/147,638, U.S.Non-Provisional patent application Ser. No. 15/145,583, U.S.Non-Provisional patent application Ser. No. 15/256,148, U.S.Non-Provisional patent application Ser. No. 15/167,458, U.S.Non-Provisional patent application Ser. No. 15/167,472, U.S.Non-Provisional patent application Ser. No. 15/167,484, U.S.Non-Provisional patent application Ser. No. 15/381,883, U.S.Non-Provisional patent application Ser. No. 15/331,204, U.S.Non-Provisional patent application Ser. No. 15/282,535, U.S. ProvisionalPatent Application Ser. No. 62/271,135 U.S. Provisional PatentApplication Ser. No. 62/268,892, U.S. Provisional Patent ApplicationSer. No. 62/322,128, U.S. Provisional Patent Application Ser. No.62/420,368, U.S. Provisional Patent Application Ser. No. 62/420,371,U.S. Provisional Patent Application Ser. No. 62/420,380, U.S.Provisional Patent Application Ser. No. 62/438,725, U.S. ProvisionalPatent Application Ser. No. 62/374,181, U.S. Provisional PatentApplication Ser. No. 62/482,062, U.S. Provisional Patent ApplicationSer. No. 62/557,551, U.S. Provisional Patent Application Ser. No.62/557,554, U.S. Provisional Patent Application Ser. No. 62/565,677,U.S. Provisional Patent Application Ser. No. 62/573,978, and U.S.Provisional Patent Application Ser. No. 62/537,737 are incorporatedherein by reference, in their entirety. Aspects of the embodiments canbe modified, if necessary, to employ systems, circuits and concepts ofthe various patents, applications and publications to provide yetfurther embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A laser projector comprising: at least one laser diode; a power source; a photodetector responsive to laser light output by the at least one laser diode; a current sensor responsive to electric current output by the power source; a beam splitter positioned and oriented to direct a first portion of laser light from the at least one laser diode along a first optical path towards the photodetector and a second portion of laser light from the at least one laser diode along a second optical path towards an output of the laser projector; a first laser safety circuit communicatively coupled to the photodetector and responsive to signals therefrom, the first laser safety circuit comprising a first switch that mediates an electrical coupling between the power source and the at least one laser diode, wherein in response to a signal from the photodetector indicative that a power of the laser light output by the at least one laser diode exceeds a first threshold, the first switch interrupts a supply of power to the at least one laser diode from the power source; and a second laser safety circuit communicatively coupled to the current sensor and responsive to signals therefrom, the second laser safety circuit comprising a second switch that mediates electrical coupling between the power source and the at least one laser diode, wherein in response to a signal from the current sensor indicative that an electric current output by the power source exceeds a second threshold, the switch interrupts a supply of power to the at least one laser diode from the power source.
 2. The laser projector of claim 1 wherein the first laser safety circuit further includes a first latch that is communicatively coupled to the photodetector and to the first switch, and wherein: a state of the first latch is responsive to signals from the photodetector and the first switch is responsive to the state of the first latch; the state of the first latch changes from a first state to a second state in response to the signal from the photodetector indicative that the power of the laser light output by the at least one laser diode exceeds the first threshold; and the first switch interrupts the supply of power to the at least one laser diode from the power source in response to the state of the first latch changing from the first state to the second state.
 3. The laser projector of claim 2 wherein the first latch is operable to store a current state selected from the first state and the second state and maintain the current state during a reboot event.
 4. The laser projector of claim 2, further comprising: a processor communicatively coupled to the at least one laser diode and to the first latch, the processor to modulate the at least one laser diode, wherein, in response to the latch being in the second state, the processor stops modulating the at least one laser diode and prevents further modulations of the at least one laser diode.
 5. The laser projector of claim 4, further comprising a non-transitory processor-readable storage medium communicatively coupled to the processor, wherein: in response to the first latch being in the second state, the processor stores a flag in the non-transitory processor-readable storage medium; and upon boot-up of the laser projector, the processor accesses the non-transitory processor-readable storage medium to check for the flag, wherein in response to the processor finding the flag stored in the non-transitory processor-readable storage medium the processor prevents modulations of the at least one laser diode.
 6. The laser projector of claim 1 wherein the second laser safety circuit further includes a second latch that is communicatively coupled to the current sensor and to the second switch, and wherein: a state of the second latch is responsive to signals from the current sensor and the second switch is responsive to the state of the second latch; the state of the second latch changes from a first state to a second state in response to the signal from the current sensor indicative that the electric current output by the power source exceeds the second threshold; and the second switch interrupts the supply of power to the at least one laser diode from the power source in response to the state of the first latch changing from the first state to the second state.
 7. The laser projector of claim 6 wherein the second latch is operable to store a current state selected from the first state and the second state and maintain the current state during a reboot event.
 8. The laser projector of claim 6, further comprising: a processor communicatively coupled to the at least one laser diode and to the second latch, the processor to modulate the at least one laser diode, wherein, in response to the second latch being in the second state, the processor stops modulating the at least one laser diode and prevents further modulations of the at least one laser diode.
 9. The laser projector of claim 8, further comprising a non-transitory processor-readable storage medium communicatively coupled to the processor, wherein: in response to second latch being in the second state the processor stores a flag in the non-transitory processor-readable storage medium; and upon boot-up of the laser projector, the processor accesses the non-transitory processor-readable storage medium to check for the flag, wherein in response to the processor finding the flag stored in the non-transitory processor-readable storage medium the processor prevents modulations of the at least one laser diode.
 10. The laser projector of claim 6, further comprising: a digital potentiometer to set the second threshold; and a comparator communicatively coupled to the digital potentiometer and communicatively coupled in between the current sensor and the latch, the comparator to compare signals from the current sensor to the second threshold set by the digital potentiometer and to control the state of the latch based on a comparison between at least one signal from the current sensor and the second threshold set by the digital potentiometer.
 11. The laser projector of claim 1 wherein the second laser safety circuit further includes a digital potentiometer to set the second threshold. 